The present invention is useful for making an abrasive article in which a structured abrasive coating is provided on a substrate. The abrasive coating comprises abrasive particles and a binder in the form of a precise, three dimensional abrasive composites molded onto the substrate.
A structured abrasive is a form of an abrasive article in which a substrate bears on a major surface thereof abrasive composites comprising a plurality of abrasive grains dispersed in a binder. The binder serves as a medium for dispersing the abrasive grains, and it may also bind the abrasive composites to the substrate. The abrasive composites have a predetermined three-dimensional shape, e.g., pyramidal. In one form, the dimensions of a given composite shape can be made substantially uniform and the composites can be disposed in a predetermined array. The predetermined array can be in linear form or matrix form.
Such a structured abrasive article can be prepared by a method generally as follows. A slurry containing a mixture of a binder precursor and a plurality of abrasive grains is applied onto a production tool having cavities which are the negative of the final shape of the abrasive composites. A substrate is brought into contact with the exposed surface of the production tool such that the slurry wets the first major surface of the substrate to form an intermediate article. Then, the binder is at least partially solidified, cured, or gelled before the intermediate article departs from the exposed surface of the production tool to form a structured abrasive article. The abrasive article is then removed from the production tool and fully cured if it was not fully cured in the previous step. Alternatively, the slurry can be applied onto the first major surface of the substrate and then the production tool can be brought into contact with the first major surface of the substrate. The precise nature of the abrasive composites provides an abrasive article that has a high level of consistency. This consistency further results in excellent performance.
Structured abrasives, and methods and apparatuses for making such structured abrasives, are described in U.S. Pat. No. 5,152,917, "Structured Abrasive Article," (Pieper et al.), issued Oct. 6, 1992, the entire disclosure of which is incorporated herein by reference. In one embodiment, Pieper et al. teaches an abrasive article comprising precisely shaped abrasive composites bonded to a backing in which the composites comprise abrasive particles and a binder. Pieper et al. teaches, among other things, a method of making the structured abrasive article generally in accordance with the method described briefly above. Pieper et al. teaches that the production tool can be a belt, a sheet, a coating roll, a sleeve mounted on a coating roll, or a die, and that the preferred production tool is a coating roll. Pieper et al. teaches that, in some instances, a plastic production tool can be replicated from an original tool by embossing a thermoplastic resin onto a metal tool, for example. Such a metal tool can be fabricated by diamond turning, engraving, hobbing, assembling as a bundle a plurality of metal parts machined in the desired configuration, or other mechanical means, or by electroforming.
Other examples of structured abrasives and methods and apparatuses for their manufacture are disclosed in U.S. Pat. No. 5,435,816, "Method of Making an Abrasive Article," (Spurgeon et al.), issued Jul. 25, 1995, the entire disclosure of which is incorporated herein by reference. In one embodiment, Spurgeon et al. teaches a method of making an abrasive article comprising precisely spaced and oriented abrasive composites bonded to a backing sheet generally in accordance with the method described briefly above. Spurgeon et al. teaches that, in addition to other procedures, a thermoplastic production tool can be made according to the following procedure. A master tool is first provided. The master tool is preferably made from metal, e.g., nickel. The master tool can be fabricated by any conventional technique, such as engraving, hobbing, knurling, electroforming, diamond turning, laser machining, etc. The master tool should have the inverse of the pattern for the production tool on the surface thereof. The thermoplastic material can be embossed with the master tool to form the pattern. Embossing can be conducted while the thermoplastic material is in a flowable state. After being embossed, the thermoplastic material can be cooled. Spurgeon et al. also teaches that the production tool can be made of a thermosetting resin or a radiation cured resin. While Spurgeon et al. mentions briefly that the master tool can be made by knurling no specific method of knurling a master tool is shown, taught, or suggested by Spurgeon et al.
Two general methods of knurling are known. Knurling is typically performed by the first knurling process, referred to as roll knurling or form knurling. Form knurling is done by pressing a knurling wheel having a pattern on the working surface thereof against a workpiece. The knurling wheel has the inverse of the pattern that is to be imparted to the workpiece. The working surface of the knurling tool is pressed against the workpiece with sufficient force to cold form or press the outer surface of the workpiece into general conformity with the pattern on the knurling wheel. The second knurling process, referred to as cut knurling, is performed by orienting the knurling wheel relative to the workpiece such that the wheel cuts a pattern into the workpiece by removing metal chips. Both conventional knurling processes typically impart a diamond-based pattern in which the diamonds are aligned in the direction perpendicular to the longitudinal axis of the cylindrical workpiece. Conventional knurling processes have also been used to impart a square-based pattern, in which the squares are oriented to have their sides at 45.degree. to the longitudinal axis of the workpiece. As with the diamond-based pattern, the square-based pattern is also aligned in the direction perpendicular to the longitudinal axis of the cylindrical workpiece. These processes are typically used to impart a non-slip pattern on a tool handle, machine control knob, or the like.
One known conventional cut knurling apparatus and method is described with reference to FIGS. 1-10. As seen in FIGS. 1-2, knurling tool 10 is used to knurl a pattern into the outer cylindrical surface 34 of workpiece 30. First knurling wheel 12 and second knurling wheel 14 are mounted onto knurling wheel holder 16. As seen in FIG. 3, tool holder 16 includes a pair of mounting posts which each comprise first portion 20 and second portion 22. Cap screw 18 is inserted through the central opening of the knurling wheel and fastened into the second portion of the mounting post 22. First and second wheels 12 and 14 are free to rotate about axes 26 and 28 respectively. The knurling wheel holder 16 has center plane of symmetry 24. The first mounting post portions 20 are parallel to plane 24. The second mounting post portions 22 are oriented at an angle from the center plane 24. This arrangement orients axis of rotation 26 of the first knurling wheel 12 at angle (a) relative to the center plane 24. Angle (a) is defined as the angle between a plane perpendicular to the plane of the page and including axis 26 and center plane 24 perpendicular to the page. The axis of rotation 28 of second wheel 14 is oriented at angle (b) relative to the center plane 24. Angle (b) is defined as the angle between a plane perpendicular to the plane of the page and including axis 28 and center plane 24 perpendicular to the page Also, as seen in FIG. 6, the orientation of the second portion of the mounting post causes the axis 26 of the first knurling wheel to be inclined towards the workpiece 30 by angle (f.sub.1). Angle (f.sub.1) is defined as the angle between a first plane tangential to the surface of the workpiece at the point of engagement of the first knurling wheel and a second plane perpendicular to the page and including axis 26. Similarly, the axis 28 of the second knurling wheel is inclined towards the workpiece 30 by angle (f.sub.2) seen in FIG. 8. Angle (f.sub.2) is defined as the angle between a first plane tangential to the surface of the workpiece at the point of engagement of the second knurling wheel and a second plane perpendicular to the page and including axis 28.
Knurling wheel 12 is illustrated in greater detail in FIGS. 9 and 10. Knurling wheel 12 has along its outer working surface a plurality of teeth 44. Each tooth 44 includes tooth ridge 48, tooth valley 50 and side surfaces 52. Wheel 12 also includes major opposed surfaces 42 (only one illustrated). Where the side surfaces 52 of the teeth 44 meet the major surface 42, an edge 46 is formed. The teeth 44 have a ridge included angle .theta.. The teeth 44 of second knurling wheel 14 are of the same configuration as the teeth of first knurling wheel 12.
One typical knurling tool 10 is available commercially from Eagle Rock Technologies Int'l Corp. of Bath, Pennsylvania, and is known as Zeus.TM. Cut-Knurling Tool No. 209. As shown in FIG. 3, this knurling tool 10 is typically provided with first and second knurling wheels 12, 14 in which the teeth 44 are oriented parallel to the respective wheel axis 26, 28. Accordingly, the teeth have an included angle (c) measured at the point of contact of the wheels with the workpiece which is the sum of angles (a) and (b), and which is centered on center plane 24. Angles (a) and (b) are typically each 30.degree., resulting in angle (c) being 60.degree.. Under this arrangement, the knurling tool 10 will form a diamond-based knurl pattern, the four-sided diamond bases having opposed 60.degree. corners and 120.degree. corners. This knurling tool 10 also is configured to allow each mounting post to rotate about the longitudinal axes of its respective first portion 20. Such rotational adjustments are calibrated to the diameter of the workpiece 30. The adjustments are intended to orient angles (a), (b), (f.sub.1) and (f.sub.2) to the particular workpiece to allow cut knurling of various sized workpieces.
The operation of known cutting tool 10 is illustrated in FIGS. 1 and 2. The mounting posts are pivoted to the appropriate calibration for the diameter of the workpiece to adjust angles (a), (b), (f.sub.1) and (f.sub.2). Workpiece 30 is rotated by a conventional lathe drive means in direction A. The tool 10 is moved towards the workpiece 30 until the desired engagement between teeth 44 and workpiece 30 is obtained. The rotation of the workpiece 30 in direction A causes the knurling wheels to rotate in the opposite direction. Tool 10 is mounted in a suitable tool drive means as is known in the art, and is traversed in direction B parallel to the longitudinal axis 36 of the workpiece 30. Accordingly, knurling begins at first end 32 of the workpiece 34, and continues in direction B toward the second end (not shown). Because the bisector of the teeth included angle (c) and the center plane 24 of the cutting tool 10 are parallel to the longitudinal axis 36 of the workpiece, the diamond-based knurl pattern is aligned in the direction perpendicular to the longitudinal axis 36 of the workpiece 30.
As mentioned above, known knurling tool 10 is capable of imparting a square-based knurl pattern in a workpiece. This is done by arranging the knurling tool as illustrated in FIG. 4. The knurling tool of FIG. 4 differs from that of FIG. 3 only in that knurling wheels 12' and 14' replace wheels 12 and 14, respectively. In first knurling wheel 12', the teeth 44 are oriented from the wheel axis 26 by first teeth incline angle (d). In second knurling wheel 14', the teeth 44 are oriented away from the wheel axis 28 by second teeth incline angle (e). It is known that angles (d) and (e) can both be oriented relative to axes 26, 28 away from the center plane 24 as illustrated, or both towards center plane 24. Accordingly, the included angle (c) formed by the teeth on each wheel is equal to the sum of angles (a) and (d) added to the sum of angles (b) and (e). With the known commercially available tool described above, angles (a) and (b) are each 30.degree., and angles (d) and (e) are each 15.degree.. This results in the teeth of wheels 12' and 14' each being oriented at 45.degree. from center plane 24. This forms an included angle (c) of 90.degree.. the bisector of which is parallel to center plane 24. The operation of the tool 10 of FIG. 4 is as described above with respect to the tool of FIG. 3.
The pattern imparted by the tool of FIG. 4 will be a square-based pattern which is aligned in the direction perpendicular to the longitudinal axis 36 of the workpiece 30. This pattern is illustrated in FIG. 13. The knurl pattern will comprise pyramids 60 extending outward from the surface of the workpiece. Pyramids 60 will have peaks 62, side edges 64, and side surfaces 66. The base of each pyramid is defined by base edges 68. It is the 90.degree. angle (c) which causes the base edges 68 to form a square. And because the angle (c) is centered on plane 24, the pyramidal pattern is aligned perpendicular to the longitudinal axis 36 of the workpiece 30. This can be seen by noting the peaks 62a, 62b of adjacent pyramids 60 are aligned on a line perpendicular to the longitudinal axis 36 of the workpiece 30.
While the just-described commercially available knurling tool is purported to be a cut knurling tool, careful observation by the present inventors has determined that, surprisingly, the second cutting wheel 14 does not cut a pattern into the workpiece by removing metal chips, but instead cold forms a pattern. In this regard, the known apparatus and method does not perform as a true cut knurling tool as that term is used herein to describe a knurling process in which both knurling wheels cut metal by removing chips. The actual operation of the known knurling method is explained with reference to FIGS. 5-8.
FIGS. 5 and 6 illustrate the orientation of first knurling wheel 12 relative to the workpiece 30. For clarity, the remainder of tool 10 is not illustrated. As seen in FIG. 11, clearance angle .alpha. is formed between the ridges 48 of teeth 44 and the workpiece surface. As seen in FIG. 3, rotation of the workpiece 30 in direction A causes first knurling wheel 12 to rotate in direction of motion M.sub.1. The workpiece rotation A can be resolved into two components: 1) wheel motion M.sub.1 ; and 2) tangential motion T.sub.1 relative to the surface of the workpiece. Tangential motion T.sub.1 is parallel to the longitudinal axis 36 of the workpiece and is in the direction to cause teeth 44 to first engage the workpiece with edge 46, thus causing cut knurling. It call be seen that tangential component of motion T.sub.1 is equal to sin(a). As angle (a) approaches zero, the tangential component T.sub.1 approaches zero, thus the relative motion of the cutting edge 46 of the knurling teeth to the workpiece surface also approaches zero.
As seen in FIG. 5, the relative motion of the workpiece and the first wheel 12 is such that the workpiece is first engaged by the leading edge 46 of each of the respective teeth 44. FIG. 11 is an enlarged partially schematic view illustrating this engagement. The relative motion is indicated by arrows C. It is the edge 46 at the intersection of teeth side surfaces 52 with major surface 42 which acts as a cutting edge to remove material from the surface 34 of the workpiece. Rake angle .beta. is seen to be inclined in the direction of travel of the cutting edge 46. This is referred to as "negative rake angle" and is not as efficient as a positive rake angle, in which the rake angle is inclined away from the direction of travel of the cutting edge. FIGS. 3, 5, 6, and 11 illustrate that first cutting wheel 12 actually performs cut knurling. This is so for sufficiently large values of angle (a) such that tangential motion T.sub.1 is large enough to cause cut knurling.
FIGS. 7 and 8 illustrate the orientation of second knurling wheel 14 relative to the workpiece 30. For clarity, the remainder of tool 10 is not illustrated. As seen in FIG. 12, clearance angle a is formed between the ridges 48 of teeth 44 and the workpiece surface. As seen in FIG. 3, rotation of the workpiece 30 in direction A causes second knurling wheel 14 to rotate in direction of motion M.sub.2. Workpiece rotation A can be resolved into two components: 1) wheel motion M.sub.2 ; and 2) tangential motion T.sub.2 relative to the surface of the workpiece. Tangential motion T.sub.2 is parallel to the longitudinal axis 36 of the workpiece, and is in the direction such that the edge 46 of the teeth 44 is not the first element of teeth 44 to engage the workpiece. It can be seen that tangential component of motion T.sub.2 is equal to sin(b). As angle (b) approaches zero, the tangential component T.sub.1 approaches zero.
As seen in FIG. 7, the relative motion of the workpiece and the second wheel 14 is such that the workpiece is first engaged by the ridge 48 of the tooth rather than the edge 46. FIG. 12 is an enlarged partially schematic view illustrating this engagement. The relative motion is indicated by arrows C. Edge 46 at the intersection of teeth side surfaces 52 with major surface 42 is actually dragged behind the direction of relative motion. Accordingly, the workpiece is first engaged by the ridge 48 away from edge 46. This causes the second wheel 14 to press or form rather than cut and remove material from the workpiece 30.
Thus it is seen that there is a need for a knurling apparatus and method which actually cut knuris a workpiece. There is also a need to provide a knurling apparatus and method in which the knurling pattern does not align itself in the direction perpendicular to the longitudinal axis of the workpiece. Additionally, there is a need to provide a workpiece that can be used to make economically an uninterrupted production tool of any desired length. There is a further need to provide a cut knurling wheel which provides a positive rake angle.